Minerals: Building Blocks of Rocks Chapter 2 Based on: Earth Science, 10e
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Minerals: Building Blocks of Rocks
Chapter 2
Based on: Earth Science, 10e
Minerals: the building blocks of rocks
Definition of a mineral • Solid • Inorganic • Natural • Crystalline Structure - Possess an orderly
internal structure of atoms • Have a definite chemical composition
Mineraloid - lacks an orderly internal structure
Minerals: the building blocks of rocks
Rocks are aggregates (mixtures) of minerals
• Aggregate implies that the minerals are joined in a way that the properties of each mineral are retained
• Some are composed of nonmineral matter
o Obsidian, pumice and coal
Composition and structure of minerals
Elements • Basic building blocks of minerals • Over 100 are known
Atoms • Smallest particles of matter • Have all the characteristics of an element
Periodic table of the Elements
How atoms are constructed
Nucleus – central part of an atom that contains • Protons – positive electrical charges • Neutrons – neutral electrical charges
Energy levels, or shells • Surround nucleus • Contain electrons – negative electrical charges
Simplified view of the atom
How atoms are constructed
Atomic number is the number of protons in an atom's nucleus
Isotopes • Have varying number of neutrons • Have different mass numbers – the sum of the neutrons
plus protons • Many isotopes are radioactive and emit energy and
particles which power Earth’s interior movements
How atoms are
constructed
Atomic Bonding
Bonding of atoms • Forms a compound with two or more elements • Ions are atoms that gain or lose electrons • A compound is a substance consisting of two or
more elements chemically combined in specific proportions.
• Compounds form when atoms are more stable in a combined form.
Atomic Bonding
Types of Chemical bonds • Ionic Bonds – form between positive and negatively
charged ions (NaCl). Rigid solids with high melting points.
• Covalent bonds – form when atoms share electrons (SiO2 & H2O). Low melting and boiling points.
• Metallic bonds – bonds formed when electrons are shared by metal ions. Sharing of the electron pool gives metals their characteristic properties.
Atomic Bonding
The properties of a chemical compound are dramatically different from the properties of the elements composing it.
• Cl green, poisonous gas
• Na soft, silvery metal that severely reacts with water
Minerals
How minerals form • 4 major processes by which minerals form.
o Crystallization by magma o Precipitation o Changes in pressure & temperature o Formation by hydrothermal solutions
Minerals
Physical properties of minerals • Crystal form - The external expression of a
mineral’s internal orderly arrangement of atoms • Luster - Appearance or quality of light reflected
from the surface of a mineral
• Metallic appearance of a metal
• Nonmetallic vitreous (glassy), pearly, silky, resinous, earthy (dull)
Minerals
• Color - An obvious, yet, unreliable property
o Slight impurities can cause a variety of colors • Streak - Color of a mineral in its powdered
form
o A more reliable indicator of color
o Determined by using a streak plate
o Metallic minerals generally have a dense, dark streak
Minerals
Hardness - A measure of the resistance of a mineral to abrasion or scratching
• Mohs Scale
o Ranks minerals from 1 – 10
o Fingernail = 2.5
o Cu penny = 3.5
o Glass, Steel = 5.5
The mineral quartz often exhibits good crystal form
Pyrite (fool’s gold) displays metallic luster
Minerals Cleavage - The tendency of a mineral to cleave,
or break, along planes of weak bonding
• Kleiben = carve • Not all minerals have definite planes of weak
bonding • Those with cleavage can be identified by the
distinctive smooth surfaces that are produced when the mineral is broken
• When minerals break evenly in more than one direction, cleavage is described by the number of planes exhibited and the angles at which they meet
Three examples of perfect cleavage – fluorite, halite,
and calcite
Minerals
Physical properties of minerals • Fracture - Occurs when minerals that do not
exhibit cleavage break
o Conchoidal fracture – smooth curved surfaces
o Most fracture irregularly
Conchoidal fracture
Minerals
– Specific gravity - Compares the weight of a mineral to the weight of an equal volume of water
– “Heft”
– Usually between 2.5 & 3
– Some metallic minerals are higher
• Galena 7.5
• Pure 24k Gold 20
Minerals
• Other properties • Taste • Smell • Elasticity • Malleability
Minerals
Physical properties of minerals • Other properties
• Feel • Magnetism • Double Refraction • Reaction to hydrochloric acid
Minerals
A few dozen minerals are called the rock-forming minerals • The eight elements that compose most rock-
forming minerals are oxygen (O), silicon (Si), aluminum (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg)
• Most abundant atoms in Earth's crust are oxygen (46.6% by weight) and silicon (27.7% by weight)
Minerals
Mineral groups • Rock-forming silicates
• Most common mineral group • Contain the silicon-oxygen tetrahedron
• Four oxygen atoms surrounding a much smaller silicon atom
• Combines with other atoms to form the various silicate structures
The silicate (SiO4)-4 molecule
Common silicate minerals
Minerals
Mineral groups • Rock-forming silicates
• Groups based upon tetrahedral arrangement • Olivine – independent tetrahedra • Pyroxene group – tetrahedra are arranged in
chains • Amphibole group – tetrahedra are arranged in
double chains
Hornblende – a member of the amphibole group
Minerals
Mineral groups • Rock-forming silicates
• Groups based upon tetrahedral arrangement • Micas – tetrahedra are arranged in sheets
• Two types of mica are biotite (dark) and muscovite (light)
• Feldspars - Three-dimensional network of tetrahedra
Minerals
Mineral groups • Rock-forming silicates
• Groups based upon tetrahedral arrangement • Feldspars
• Two types of feldspar are Orthoclase and Plagioclase
• Quartz – three-dimensional network of tetrahedra
Potassium feldspar
Plagioclase feldspar
Minerals
Mineral groups • Rock-forming silicates
• Feldspars are the most plentiful mineral group • Crystallize from molten material
• Nonsilicate minerals • Major groups
• Oxides • Sulfides
Minerals
Mineral groups • Nonsilicate minerals
• Major groups • Sulfates • Carbonates • “Native” elements
Native Copper
Minerals
Mineral groups • Nonsilicate minerals
• Carbonates • A major rock-forming group • Found in the rocks limestone and marble
• Halite and gypsum are found in sedimentary rocks • Many have economic value
Some common non-silicate minerals
Minerals
Mineral resources • Reserves are already identified deposits • Ores are useful metallic minerals that can be
mined at a profit • Economic factors may change and influence a
resource
An underground halite (salt) mine
The Bingham copper mine in Utah
End of Chapter 1
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